A usual slide fastener has a pair of left and right fastener stringers of which left and right facing side edge portions are provided with element rows, respectively, a slider configured to open and close the pair of element rows, and an opener provided at one end portion in a front-rear direction, which is a longitudinal direction of the pair of fastener stringers, in the vicinity of the pair of element rows. The opener generally has a separable pin provided at one fastener stringer of the pair of fastener stringers and a retainer provided at the other fastener stringer, and the retainer is formed with a separable pin hole for inserting one end portion of the separable pin on a surface (a front surface) facing the slider. The usual slider is configured to open and close the left and right fastener stringers by moving (advancing/retreating) the slider.
Also, a slider fastener has been known which can open (a state where the pair of element rows is not meshed with each other) the left and right fastener stringers by applying an external force to the left and right fastener stringers in the vicinity of the slider (more specifically, applying a pulling force for separation in a right-left direction) to remove one element row from the slider so as to open the left and right fastener stringers in a closed state (a state where the pair of element rows is meshed with each other) without moving the slider (Patent Document 1).
According to the fastener stringer, when the left and right fastener stringers are opened by the applied external force, the external force is applied not only to the pair of element rows but also to the opener. More specifically, after the pair of element rows is pulled apart and separated in the right-left direction, the external force is applied to the separable pin and retainer configuring the opener, so that the separable pin comes out of the separable pin hole while colliding with a sidewall covering a side surface of the separable pin hole of the retainer.
However, when the separable pin collides with the sidewall of the retainer while the separable pin comes out of the separable pin hole of the retainer, since the sidewall of the retainer completely interrupts lateral movement of the separable pin in a lateral direction, a separation property between the retainer and the separable pin is deteriorated and breakage of the retainer is caused. Therefore, the opener is required to have a structure capable of improving the separation property between the retainer and the separable pin to prevent the breakage of the retainer. In the meantime, the opener is originally required to have such a strength (hereinafter, referred to as ‘lateral pulling strength of the opener’) that the opener is not broken even when the external force is applied to the pair of fastener stringers of the slide fastener in the closed state from left and right sides in the vicinity of the opener.
An opener that may satisfy the above requirements to some extent has been known in which a tape groove is formed at a central portion in a width direction of the sidewall covering a side of the separable pin hole of the retainer and a groove width of an entrance-side (an entrance-side in a depth direction of the separable pin hole) of the tape groove is formed wider than an inner side (an inner side in the depth direction of the separable pin hole) (Patent Document 2).
More specifically, a pair of wall parts arranged at both sides of the tape groove are formed within a range from an inner position relative to an entrance of the separable pin hole to a bottom wall, not at the same position as the entrance of the separable pin hole. Therefore, in a case of the slide fastener having the opener, when pulling out the separable pin from the retainer by applying the external force, if the separable pin is pulled out from the separable pin hole to the portion at which the groove width of the tape groove is wide, it is thought that the separable pin can be easily moved in the lateral direction thereafter.